The present invention relates to chromatography and electrophoresis analysis, particularly to a method of sample injection into a number of horizontal separation/analysis channels, and more particularly to an improved method that enables the efficient introduction of analyte samples wherein the amount of sample is significantly reduced and a means of sample stacking is provided.
Chromatography and electrophoresis analysis systems use columns filled with various media to separate analytes based on differing analyte mobilities due to an applied electric field. In all cases the introduction of sample is paramount to achieving quality results. Specifically, samples containing multiple analytes must be introduced in a tight zone to achieve high separation resolution. Discrete capillary systems have addressed this issue by using a time gated electrokinetic injection process whereby the lead end of the capillary is suspended vertically into a sample vial that contains the sample resuspended in a loading buffer. An electrode is placed into the loading buffer and a potential is applied on the order of seconds to drive the sample into the capillary. Typically it takes on the order of 5 microliters of sample solution to permit the required electrical contact to drive the sample. Once the sample has been introduced, the capillary is removed from the sample loading buffer and placed in a running buffer for the extent of the analysis. Due to the high costs of sample preparation, particularly in massively parallel applications such as DNA sequencing, there has been a need to reduce the amount of sample solution required to inject a small amount of sample into the separation/analysis channels.
The present invention provides a method for reducing the typical use of 5 microliters of sample solution to an amount of under 0.2 microliters, thus providing a great cost savings in sample preparation. Basically, the method of the present invention comprises a modified electrokinetic sample injection procedure, which involves preparation of the input of the separation channel, the physical sample introduction, and subsequent removal of excess material. This method is very useful for high throughput analysis systems such as DNA sequencing, and it will enable uniquely controllable sample stacking for increased loading efficiency electrophoresis.